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Publication# Hydraulic soil failure due to artesian ground conditions during the construction of a hydro electrical power plant on Sakarya river

Résumé

The presence of an artesian aquifer lying under the construction site of a hydro-electrical power plant had not been considered in the design project. The foreseen excavation works could not be carried out due to a high risk of hydraulic heave of the excavation pit bottom and the entire plant had to be relocated. In the scope of this thesis, two alternative solutions to deal with the local artesian conditions are suggested. The first solution considers additional resisting shear forces coming from cohesion in clayey soils, whereas in usual design approaches for hydraulic heave problems only the equilibrium between gravity forces and seepage forces is established. Cohesion plays an important role for the stability of relatively small excavation pit widths and its beneficial effect could be used by applying a stepwise excavation process. The second solution suggests a local relief of artesian pressures in the zone of the construction site in order to temporarily create a neutralized zone until the power plant is completely built.

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Philippe Allenbach, François Avellan, Christophe Nicolet, Alain Sapin, Jean-Jacques Simond

An analytical approach allowing modelling transient phenomena in pipes, valves, surge tanks and Francis turbines based on impedance method is developed. These models are implemented in a software called “SIMSEN”, which simulates the behaviour of complex applications in the domain of adjustable speed drives and electrical power networks. This program is based on a modular structure, which enables the numerical simulation of transient modes of systems exhibiting arbitrary topologies. The numerical simulation for transient phenomena in hydropower plants with “SIMSEN” has the benefit of an algorithm that generates and solves an integrated set of differential equations. This algorithm solves simultaneously the electrical, hydraulic and control equations ensuring a proper interaction between the three parts of the system. The case of a Francis turbine power plant is studied. The model of the turbine is based on measured steady state characteristics. The simulation of the dynamic behaviour of the power plant under load variation is investigated

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Philippe Allenbach, François Avellan, Alain Sapin, Jean-Jacques Simond

An analytical approach allowing modelling transient phenomena in pipes, valves, surge tanks and Francis turbines based on impedance method is developed. These models are implemented in a software called “SIMSEN”, which simulates the behaviour of complex applications in the domain of adjustable speed drives and electrical power networks. This program is based on a modular structure, which enables the numerical simulation of transient modes of systems exhibiting arbitrary topologies. The numerical simulation for transient phenomena in hydropower plants with “SIMSEN” has the benefit of an algorithm that generates and solves an integrated set of differential equations. This algorithm solves simultaneously the electrical, hydraulic and control equations ensuring a proper interaction between the three parts of the system. The case of a Francis turbine power plant is studied. The model of the turbine is based on measured steady state characteristics. The simulation of the dynamic behaviour of the power plant under load variation is investigated.

2002In this present work, a life cycle assessment is realized on Solar Two, a test project of a solar tower thermal power plant. The aim of this study is to quantify the impacts on the environment associated with all the stages from cradle-to-grave (production, use and end of life). The ﬁrst step is to deﬁne the scope of the study: objectives, function, functional unit and system limit. Secondly, an inventory of all material, processes and energy required for the system will be made to determine relevant energy and material inputs and environmental releases which represent all the substances emitted into air, soil and water for the entire life cycle. Finally, the last two steps are the impacts analyze, which evaluates the potential impacts associated with inputs and releases, and the interpretation. The most interesting result of this analyze shows that 80% of ecological impacts are due to the steel production used to build the heliostats. Furthermore, the impact of the transmission network, material transport, potassium nitrate and mirrors are not negligible despite that their role is smaller than the steel. The variation of the steel impact is analyzed for diﬀerent solar power plants which have a optimized cost for a speciﬁc thermal power. The result shows that the steel impact decreases with the increase of the thermal power. Moreover, comparing two identical thermal power, the most expensive plant is the most ecological. Finally, the Solar Two impact was compared with other types of power plants. Coal, natural gas and nuclear power plant have, as expected, more negative eﬀect on the environment. Concerning the renewable energy, wind and hydro power plant emit around 10% less impact on the four damages categories. Only the photovoltaic impacts are similar to Solar Two with a equivalent eﬃciency. Further improvements of this LCA could now carry out. For example, the amount of steel used in the heliostats should be technically reduced or substituted by recycled steel or a material with less impact. The storage, the tower and the mirror number should also be optimized to minimize the damages on the environment. A thermo-environomic optimization is also required to ﬁnd the perfect future competitive solar tower thermal power plant.

2010